One prior art toothbrush exhibiting a resiliently flexible joint between the brush head and the handle is disclosed in U.S. Pat. No. 4,520,526 issued to Peters on June 4, 1985. The disclosed means for providing the flexible joint in the Peters patent comprises either: (1) removing part of the material from the top portion and part of the material from the bottom portion of the handle to form an area of reduced cross-section; or (2) forming a hollow in the handle which extends horizontally in the area connecting the handle to the brush head. The horizontally extending hollow forms a thin flexible top member and a thin flexible bottom member which, for the purpose of the present application, are hereinafter referred to as beams. Application of force to the handle of the Peters toothbrush by the user during brushing results in bending of the flexible members or beams in direct response to the applied force, thereby further limiting the amount of brushing force which can be applied to the user's teeth and gums as the deflection of the brush head increases, at least until such time as the innermost surfaces of the flexible beams contact one another. However, a serious problem posed by the aforementioned Peters toothbrush is that soft oral tissue can be pinched between the flexible members, particularly as the top member bends and moves closer toward the lower member.
Commonly assigned, concurrently, filed U.S. patent application Ser. No. 663,214 filed Mar. 1, 1991 in the name of Robert S. Dirksing and entitled TOOTHBRUSH EMPLOYING RESILIENTLY BUCKLING ARCH TO INDICATE EXCESSIVE BRUSHING PRESSURE, the disclosure of which is hereby incorporated herein by reference, discloses a toothbrush employing an improved resiliently deformable twin beam structure which functions not as a force limiting device, as in the case of the aforementioned Peters toothbrush, but as an excessive brushing force indicator. Unlike the toothbrush of Peters, the twin beam structure disclosed in the commonly assigned concurrently filed U.S. Patent Application of Robert S. Dirksing comprises an upwardly convex back side beam which substantially prevents deformation of the brush head relative to the brush handle until a predetermined brushing force is exceeded, at which time the upwardly convex beam undergoes resilient deformation and abruptly buckles. The abrupt buckling of the back side beam in the twin beam structure may also cause pinching of soft oral tissue which enters the gap between the individual beams. Although it is not intended that the user continue brushing with the latter toothbrush in its buckled condition, continued brushing with the twin beam structure in its buckled condition can also produce pinching of soft oral tissue in the wedge shaped openings which are formed near the contact point between the innermost surfaces of the beams.
Thus, while the forgoing toothbrushes behave quite differently in use, they both exhibit a similar problem in use, namely pinching of the user's soft oral tissue during the brushing process.